BACKGROUND
[0001] Inlet air filtration systems are generally employed for use with gas turbines and
operate by removing salt, dust, corrosives and water (hereinafter referred to as "foreign
matter") from inlet air in order to prevent their entry into the gas turbine. Foreign
matter can enter the gas turbines in various forms, such as solids (i.e., dry salt)
or aqueous solutions (i.e., wet salt), and corrode the gas turbine elements. This
corrosion could lead to operational inefficiencies or failures and financial losses.
As such, it is typically necessary to provide for corrosion mitigation to the gas
turbine engine by way of an inlet filtration system that reduces the amount of corrosives
entering the gas turbine.
[0002] The corrosives can exist in several states which can enter the gas turbine. The first
state includes Solid Particulate Corrosive elements. These include salt and oxide
particles which can be removed by high efficiency filters. The second state includes
Liquid, or, rather, Aqueous Corrosives elements. These include aqueous chlorides or
acids, the removal of which cannot generally be efficiently accomplished by particulate
filters.
[0003] In both cases, the corrosives can be moved along airflow by, typically, two main
transfer mechanisms. These include solid salts deposited on particulate filters that
can deliquesce when the humidity of ambient air rises beyond about 60% relative humidity
(RH) or when filter elements get wet and salts, which are dissolved via rain, fog,
mist and other sources of water, enter the inlet air stream. Once salt solutions pass
the final filters, there is a potential for the liquid to dry and for salt to precipitate
out of solution. This salt precipitate or crystallized salt can now enter the gas
turbine.
[0004] Current filtration systems available on the market specifically for salt and water
removal are generally classified into 3-stage systems and barrier-type systems. The
3-stage systems include a first vane/moisture separator, as a first stage, coalescing
filters, as a second stage, and a second vane separator or a water tight high efficiency
filter, as a third stage. The coalescing filter captures small salt aerosol droplets
and causes them to coalesce into larger droplets and which can then be drained off
as salt water. The coalescing filter also removes dust and dry salt particles from
the inlet air which may be less than 1 micron in diameter and hydroscopic. The third
stage removes any remaining droplets from the airstream, such as droplets that form
from dry salt particles filtered by the coalescing filter, which take on water from
humid inlet air and which are re-released into the airstream.
[0005] In a relatively dry environment in which the 3-stage system is used, a vane separator
can be used as final stage, and dry salt particles may accumulate on the rear of the
coalescing filter. These dry salt particles can then take on water from the humid
inlet air and be re-released into the airstream as droplets that are not large enough
to be removed by the second vane separator but which can lead to salt accumulation
on the gas turbine elements.
[0006] In the barrier-type systems, there are typically two stages of filtration. The first
stage is a coalescing pre-filter, which captures and coalesces droplets from the airflow.
A large portion of the water drains away, but some is re-released into the airstream.
The second, final stage comprises a watertight high efficiency filter, which is watertight
and allows air, but not water, to pass through. This captures both dry and wet salt
and fine particulate. There is no third stage vane separator within this system.
[0007] In practice, barrier-type systems rely on a 100% effectiveness of the filter frame
and media seal to prevent salt water proceeding to the gas turbine. This is achievable
on new and clean filtration systems on small gas turbines with few filters, but requires
maintenance to keep it working properly and becomes impractical to scale on larger
machines. Therefore, while the barrier-type system can be effective at stopping the
migration of salt toward the gas turbine elements, the primary failure mode is seen
as being the sealing mechanism, if installation and maintenance is carried out incorrectly.
BRIEF DESCRIPTION
[0008] In accordance with an aspect of the invention, a system for use with an inlet of
a gas turbine through which airflow toward the gas turbine proceeds is provided and
includes a first stage to remove primary aerosol droplets from the airflow by coalescing
the primary aerosol droplets into secondary aerosol droplets, which are larger than
the primary aerosol droplets, and to remove solid particulates from the airflow, a
second water tight stage, disposed downstream from the first stage, to prevent the
secondary aerosol droplets and aqueous solutions of deliquesced particulates, which
are not removed by the first stage and which are re-released into the airflow from
the first stage, from proceeding along the airflow and to remove solid particulates
not removed by the first stage from the airflow, and a third water removal stage,
disposed downstream from the second stage, to remove from the airflow the remaining
secondary aerosol droplets leaking from the first and second stages.
[0009] In accordance with another aspect of the invention, a method of filtering an airflow
of inlet air in an inlet housing of a gas turbine is provided and includes, at a first
stage, removing primary aerosol droplets from the airflow by coalescing the primary
aerosol droplets into secondary aerosol droplets, which are larger than the primary
aerosol droplets, and removing solid particulates from the airflow, at a second water
tight stage, downstream from the first stage, preventing the secondary aerosol droplets
and aqueous solutions of deliquesced particulates, which are not removed by the first
stage and which are re-released into the airflow from the first stage, from proceeding
along the airflow and removing solid particulates not removed by the first stage from
the airflow, and, at a third water removal stage, downstream from the second stage,
removing from the airflow the remaining secondary aerosol droplets leaking from the
first and second stages.
[0010] In accordance with yet another aspect of the invention, a system for use with an
inlet of a gas turbine through which airflow toward the gas turbine proceeds is provided
and includes a first stage to remove primary aerosol droplets from the airflow by
coalescing the primary aerosol droplets into secondary aerosol droplets, which are
larger than the primary aerosol droplets, an intermediate stage to remove solid particulates
from the airflow, a second water tight stage, disposed downstream from the intermediate
stage, to prevent the secondary aerosol droplets and aqueous solutions of deliquesced
particulates, which are not removed by the first stage and which are re-released into
the airflow from the first stage, from proceeding along the airflow and to remove
solid particulates not removed by the first stage from the airflow, and a third water
removal stage, disposed downstream from the second stage, to remove from the airflow
the remaining secondary aerosol droplets leaking from the first stage, the intermediate
stage and the second stage.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] The subject matter regarded as the invention is particularly pointed out and distinctly
claimed in the claims at the conclusion of the specification. The foregoing and other
aspects, features, and advantages of the invention are apparent from the following
detailed description taken in conjunction with the accompanying drawings in which:
[0012] FIG. 1 is a side sectional view of a system for an inlet through which airflow is
defined according to an embodiment of the invention;
[0013] FIG. 2 is a side sectional view of a system for an inlet through which airflow is
defined according to another embodiment of the invention;
[0014] FIG. 3 is a side sectional view of a system for an inlet through which airflow is
defined according to another embodiment of the invention;
[0015] FIG. 4 is a side sectional view of a system for an inlet through which airflow is
defined according to another embodiment of the invention;
[0016] FIG. 5 is a side sectional view of a system for an inlet through which airflow is
defined according to another embodiment of the invention; and
[0017] FIG. 6 is a side sectional view of a system for an inlet through which airflow is
defined according to another embodiment of the invention.
DETAILED DESCRIPTION
[0018] With reference to FIG. 1, a system 10 for an inlet of, e.g., a gas turbine, is provided.
Here the gas turbine may have an approximate air flow range of about 50 Lb/sec to
about 2000 Lb/sec in which airflow A proceeds toward the gas turbine at a range of
approximate velocities of about 300 ft/min (91 meters/min) to about 3,000 ft/min (914
meters/min). The inlet includes an inlet duct 20 along which the airflow A travels
toward elements of the gas turbine, such as the turbine, the compressor and the combustor,
to provide for a supply of coolant and combustible air to the gas turbine which is
significantly free of particles in a solid state (i.e., dry particles) and aqueous
solutions that could lead to an accumulation of corrosive deposits on those elements.
A silencer section 21 is disposed within the inlet duct 20 to dampen noise generated
within the gas turbine.
[0019] The inlet further includes a filter house module 40 and a transition duct 30 disposed
between the inlet duct 20 and the filter house module 40. The transition duct 30 has
a width W1 where it is fluidly coupled to the inlet duct 20 and a width W2, which
may be wider than width W1, where it is fluidly coupled to the filter house module
40.
[0020] The filter house module 40 can be embodied as a duct or, more generally, as a duct
housing that is fluidly coupled to the transition duct 30 and which serves as an end
of the inlet of the system 10. As such, the airflow A initially passes through the
filter house module 40 on its way toward the gas turbine elements. The filter house
module 40 may be serviced by an operator via access point 41. As shown in FIG. 1,
the filter house module 40 further supports at least the first stage 50, the second
stage 60 and third stage 70 of the system 10.
[0021] The first stage 50 of the system 10 may include a coalescing filter utilizing depth
loading media. The first stage 50 has two primary operational modes. In accordance
with a first one of these operational modes, the coalescing filter removes relatively
small aerosol droplets, such as salt aerosol droplets, from the airflow A and coalesces
them into much larger aerosol droplets that may be greater than 20 microns in diameter.
This coalescing process allows for drainage of a relatively large portion of liquid,
e.g., salt water, rain, fog, mist or condensate, out and away from the airflow A.
[0022] In accordance with a second one of the operational modes, the coalescing filter also
serves as a pre-filter, an efficiency of which may be such that the coalescing filter
captures and/or removes solid coarse particulates having diameters of at least 5 microns
from the airflow A. The coalescing filter, therefore, serves to extend a lifecycle
of the later stages of the system 10 with the aim of ensuring that a service schedule
of the coalescing filter can be coordinated with scheduled shutdowns of the gas turbine.
With this said, it is noted that, given its position upstream from the second and
third stages 60, 70, the coalescing filter can be serviced with the gas turbine on
line.
[0023] The coalescing filter of the first stage 50 could be provided as a combined coalescer/pre-filter,
as one product, or a separate coalescer and a separate pre-filter, as possible and/or
necessary.
[0024] Due to the coalescing filter utilizing depth loading media, a risk of the coalescing
filter becoming clogged when captured particulates expand due to their taking on water
is reduced.
[0025] The second stage 60 of the system 10 may include a water tight filter, disposed downstream
from the first stage 50, that prevents liquid or aqueous solutions of deliquesced
or dissolved particles or dry/solid salt particles from the rear of the coalescing
filter of the first stage 50 that have been re-released into the airflow A from the
first stage from proceeding along the airflow A and which also removes fine dry/solid
particles from the airflow A. To this end, the water tight filter of the second stage
60 may be mounted with, e.g., an oblique angle with respect to a direction of the
airflow A, such that a tip thereof points toward the on-coming airflow A. With this
configuration, any water or liquid captured by the filter is caused to drain away
from the airflow A. Since the second stage 60 is water tight, even if captured particles,
such as salt or any other normally hydroscopic particles, deliquesce the newly fomed
resultant aqueous solution cannot proceed downstream past the water tight filter.
[0026] In accordance with embodiments, the filtration efficiency of the water tight filter
of the second stage 60 is such that it removes both the fine dust particulates that
penetrate the first stage 50 and any fine dry salt particulates in the atmosphere
from the airflow A.
[0027] In accordance with further embodiments, the water tight filter of the second stage
60 may include fiberglass, or some other suitable filtering material, and may have
a coating made from a hydrophobic material, or some other suitable water tight coating
material.
[0028] The third stage 70 of the system 10 may include a vane separator or, rather, a moisture
eliminator, disposed downstream from the second stage 60, that serves to remove droplets
from the airflow A and which is virtually 100% efficient at removing droplets larger
than 20 microns from the airflow A. The vane separator of the third stage 70 is included
in the system 10 to provide an added level of protection for the gas turbine against
liquids and/or aqueous solutions leaking past the first and the second stages 50 and
60. For example, the third stage 70 provides for protection in case the second stage
60 fails, if seals and/or gaskets of the second stage 60 fail and/or in a case of
an incorrect installation of the second stage 60.
[0029] The system 10 may further include a drainage system 110 for use with at least the
second and third stages 60 and 70 or, more generally, for use on a clean air side
of the inlet. The drainage system 110 allows water to be drained out of the filter
house module 40 and away from the second and third stages 60 and 70 while, at the
same time, preventing an air bypass and preventing unfiltered air from entering the
inlet. In an embodiment, this can be achieved by a loop seal drain or some other suitable
system.
[0030] In other embodiments, the drainage system 110 may include a baffled drainage box
that prevents an occurrence of an air bypass through the drainage system 110. Here,
in an example, water from the vane separator of the third stage 70 drains into a top
and upstream side of the drainage box which includes a feed water connection point
and a control valve that controls a flow rate of the feed water. The vane separator
water exits from an upper and downstream side of the drainage box. A baffle separates
the upstream from downstream side of the drainage box, is attached to the top of the
drainage box and extends downwards therein. A gap at the floor of the drainage box
allows the feed water to enter into the downstream side. The drainage box may also
be equipped with water level instrumentation that allows the drainage box to be filled
with the feed water when/if the water level is near a height of the baffle.
[0031] Although it is shown in the figures as being in operational communication with the
second and third stages 60 and 70, it is noted that embodiments of the drainage system
110 exist that can provide for drainage of the first stage 50, as described above,
and or any other stage/filter disposed within the filter house module 40.
[0032] In accordance with additional embodiments, the system 10 may further include a weather
hood 80, which is disposed upstream from the first stage 50 to provide for protection
of at least the gas turbine and the above-discussed features from rain. The weather
hood 80 may itself include individual treatments 81 that can be disposed and/or angled
to withstand a relatively large portion of the rain in the atmosphere around the system
10.
[0033] With reference to FIGS. 2 and 3, it is noted that the system 10 may further alternately
include a fourth stage 90, which includes an upstream vane separator to operate in
a similar manner as the vane separator of the third stage 70, in environments with
high moisture content, or an anti-icing system 100 that prevents the formation of
ice on the other filters in cold environments. Such an anti-icing system 100 may include
any one or more of a hot water coil, a steam coil or hot compressed air, which is
bled from the compressor of the gas turbine. With reference to FIG. 4, it is noted
that the fourth stage 90 and the anti-icing system 100 can be employed together with
both being disposed upstream from the first stage 50.
[0034] Where the first through third stages, 50, 60 and 70 and/or the fourth stage 90 are
included in the system 10, it is seen that the combinations of the stages provide
for additional resistance to sound waves emanating out of the gas turbine. As such,
a proportional decrease in a size of the silencer section 21 of the inlet duct 20
is possible. Thus, a corresponding decrease in manufacturing costs is also possible.
[0035] In accordance with various embodiments, spacing between the various stages of the
system 10 may be up to, at least, about 30 ft (9.1 meters) to provide for maintenance
access and to enable any drops of water to fall onto the walkway of the filter house
module 40 and to thereby maximize the water removal efficiency of the system.
[0036] As shown in FIGS. 5 and 6, the weather hood 80 is optional and need not be included
in each configuration. For example, for the configurations shown in FIGS. 5 and 6,
where the upstream vane separator of the fourth stage 90 is employed, the upstream
vane separator and/or the combination of the upstream vane separator/anti-icing system
100 combination can provide for protection of at least the gas turbine and the above-discussed
features from rain.
[0037] With reference to FIGS. 1-6, in accordance with another aspect of the invention,
a method of filtering an airflow of inlet air in an inlet housing of a gas turbine
is provided and includes, at a first stage, removing primary aerosol droplets from
the airflow by coalescing the primary aerosol droplets into secondary aerosol droplets,
which are larger than the primary aerosol droplets, and removing solid particulates
from the airflow, at a second water tight stage, downstream from the first stage,
preventing the secondary aerosol droplets and aqueous solutions of deliquesced particulates,
which are not removed by the first stage and which are re-released into the airflow
from the first stage, from proceeding along the airflow and removing solid particulates
not removed by the first stage from the airflow, and, at a third water removal stage,
downstream from the second stage, removing from the airflow the remaining secondary
aerosol droplets leaking from the first and second stages.
[0038] The method may further include angling a weather hood upstream from the first stage
to provide for protection from rain, preventing downstream ice formation by an anti-icing
system disposed upstream from the first stage, and removing the majority of droplets
having diameters greater than 20 microns from the airflow, downstream from the anti-icing
system.
[0039] The system 10 and methods described herein describe a filter system that is capable
of removing both dry and wet salts (as well as other corrosive elements), such as,
at least, NaCl, sulphates, and/or other chlorides from the airflow A relatively effectively
with a high degree of robustness. As such, the system 10 can be employed for use with
gas turbines that are generally land based in coastal locations, inland locations,
or locations exposed to high concentrations of corrosive contaminants.
[0040] While the disclosure has been described with reference to exemplary embodiments,
it will be understood by those skilled in the art that various changes may be made
and equivalents may be substituted for elements thereof without departing from the
scope of the disclosure. In addition, many modifications may be made to adapt a particular
situation or material to the teachings of the disclosure without departing from the
essential scope thereof. Therefore, it is intended that the disclosure not be limited
to the particular exemplary embodiment disclosed as the best mode contemplated for
carrying out this disclosure, but that the disclosure will include all embodiments
falling within the scope of the appended claims.
[0041] Aspects of the present invention are defined in the following numbered clauses:
- 1. A system for use with an inlet of a gas turbine through which airflow toward the
gas turbine proceeds, the system comprising:
a first stage to remove primary aerosol droplets from the airflow by coalescing the
primary aerosol droplets into secondary aerosol droplets, which are larger than the
primary aerosol droplets, and to remove solid particulates from the airflow;
a second water tight stage, disposed downstream from the first stage, to prevent the
secondary aerosol droplets and aqueous solutions of deliquesced particulates, which
are not removed by the first stage and which are re-released into the airflow from
the first stage, from proceeding along the airflow and to remove solid particulates
not removed by the first stage from the airflow; and
a third water removal stage, disposed downstream from the second stage, to remove
from the airflow the remaining secondary aerosol droplets leaking from the first and
second stages.
- 2. The system according to clause 1, wherein the first stage comprises a coalescing
filter utilizing depth loading media.
- 3. The system according to clause 1 or clause 2, wherein the secondary aerosol droplets
have diameters of at least 20 microns.
- 4. The system according to any one of the preceding clauses, wherein the solid particulates
removed from the airflow by the first stage have diameters of at least 5 microns.
- 5. The system according to any one of the preceding clauses, wherein the second stage
comprises a water tight filter mounted in the inlet at an oblique angle with respect
to a direction of the airflow.
- 6. The system according to clause 5, wherein the water tight filter comprises fiberglass
and/or a hydrophobic coating or layer, which is impermeable to water but allows air
to pass through.
- 7. The system according to any one of the preceding clauses, wherein the remaining
secondary aerosol droplets leaking from the first and second stages and removed from
the airflow by the third water removal stage have diameters greater than 20 microns.
- 8. The system according to any one of the preceding clauses, further comprising a
weather hood disposed upstream from the first stage to provide for protection from
rain.
- 9. The system according to any one of the preceding clauses, further comprising an
anti-icing system, including any one or more of a hot water coil, a steam coil or
hot compressed air, disposed upstream from the first stage to prevent downstream ice
formation.
- 10. The system according to clause 9, further comprising an upstream vane separator,
disposed downstream from the anti-icing system, to remove a majority of aerosol droplets
having diameters greater than 20 microns from the airflow.
- 11. The system according to any one of the preceding clauses, further comprising an
upstream vane separator, disposed upstream from the first stage, to remove aerosol
droplets having diameters greater than 20 microns from the airflow.
- 12. The system according to clause 11, wherein the first through the third stages
and the upstream vane separator provide noise attenuation for the gas turbine.
- 13. The system according to any one of the preceding clauses, wherein the first, second
and third stages cooperatively remove at least NaCl, sulphates, and/or chlorides from
the airflow.
- 14. The system according to any one of the preceding clauses, further comprising a
drainage system disposed within a clean air side of the inlet to prevent an air bypass
therethrough.
- 15. A method of filtering airflow of inlet air in an inlet housing of a gas turbine,
the method comprising:
at a first stage, removing primary aerosol droplets from the airflow by coalescing
the primary aerosol droplets into secondary aerosol droplets, which are larger than
the primary aerosol droplets, and removing solid particulates from the airflow;
at a second water tight stage, downstream from the first stage, preventing the secondary
aerosol droplets and aqueous solutions of deliquesced particulates, which are not
removed by the first stage and which are re-released into the airflow from the first
stage, from proceeding along the airflow and removing solid particulates not removed
by the first stage from the airflow; and
at a third water removal stage, downstream from the second stage, removing from the
airflow the remaining secondary aerosol droplets leaking from the first and second
stages.
- 16. The method according to clause 15, further comprising angling a weather hood upstream
from the first stage to provide for protection from rain.
- 17. The system according to clause 15 or clause 16, further comprising preventing
downstream ice formation by an anti-icing system disposed upstream from the first
stage.
- 18. The system according to clause 17, further comprising removing a majority of aerosol
droplets having diameters greater than 20 microns from the airflow upstream from the
anti-icing system.
- 19. The system according to any one of clauses 15 to 18, further comprising removing
aerosol droplets having diameters greater than 20 microns from the airflow downstream
from the first stage.
- 20. A system for use with an inlet of a gas turbine through which airflow toward the
gas turbine proceeds, the system comprising:
a first stage to remove primary aerosol droplets from the airflow by coalescing the
primary aerosol droplets into secondary aerosol droplets, which are larger than the
primary aerosol droplets;
an intermediate stage to remove solid particulates from the airflow;
a second water tight stage, disposed downstream from the intermediate stage, to prevent
the secondary aerosol droplets and aqueous solutions of deliquesced particulates,
which are not removed by the first stage and which are re-released into the airflow
from the first stage, from proceeding along the airflow and to remove solid particulates
not removed by the first stage from the airflow; and
a third water removal stage, disposed downstream from the second stage, to remove
from the airflow the remaining secondary aerosol droplets leaking from the first stage,
the intermediate stage and the second stage.
1. A system (10) for use with an inlet of a gas turbine through which airflow (A) toward
the gas turbine proceeds, the system comprising:
a first stage (50) to remove primary aerosol droplets from the airflow by coalescing
the primary aerosol droplets into secondary aerosol droplets, which are larger than
the primary aerosol droplets, and to remove solid particulates from the airflow;
a second water tight stage (60), disposed downstream from the first stage (50), to
prevent the secondary aerosol droplets and aqueous solutions of deliquesced particulates,
which are not removed by the first stage and which are re-released into the airflow
from the first stage, from proceeding along the airflow and to remove solid particulates
not removed by the first stage from the airflow; and
a third water removal stage (70), disposed downstream from the second stage (60),
to remove from the airflow the remaining secondary aerosol droplets leaking from the
first and second stages (50, 60).
2. The system (10) according to claim 1, wherein the first stage (50) comprises a coalescing
filter utilizing depth loading media.
3. The system (10) according to claim 1 or claim 2, wherein the second stage (60) comprises
a water tight filter mounted in the inlet at an oblique angle with respect to a direction
of the airflow.
4. The system (10) according to claim 3, wherein the water tight filter comprises fiberglass
and/or a hydrophobic coating or layer, which is impermeable to water but allows air
to pass through.
5. The system (10) according to any one of the preceding claims, further comprising a
weather hood (80) disposed upstream from the first stage to provide for protection
from rain.
6. The system (10) according to any one of the preceding claims, further comprising an
anti-icing system (100), including any one or more of a hot water coil, a steam coil
or hot compressed air, disposed upstream from the first stage (50) to prevent downstream
ice formation.
7. The system (10) according to any one of the preceding claims, wherein the first through
the third stages (50, 60, 70) and the upstream vane separator provide noise attenuation
for the gas turbine.
8. The system (10) according to any one of the preceding claims, further comprising a
drainage system (100) disposed within a clean air side of the inlet to prevent an
air bypass therethrough.
9. A method of filtering airflow of inlet air in an inlet housing of a gas turbine, the
method comprising:
at a first stage (50), removing primary aerosol droplets from the airflow by coalescing
the primary aerosol droplets into secondary aerosol droplets, which are larger than
the primary aerosol droplets, and removing solid particulates from the airflow;
at a second water tight stage (60), downstream from the first stage (50), preventing
the secondary aerosol droplets and aqueous solutions of deliquesced particulates,
which are not removed by the first stage (50) and which are re-released into the airflow
from the first stage (50), from proceeding along the airflow and removing solid particulates
not removed by the first stage (50) from the airflow; and
at a third water removal stage (70), downstream from the second stage (60), removing
from the airflow the remaining secondary aerosol droplets leaking from the first and
second stages (50, 60).
10. The method according to claim 9, further comprising angling a weather hood upstream
from the first stage to provide for protection from rain.
11. The system according to claim 9 or claim 10, further comprising preventing downstream
ice formation by an anti-icing system disposed upstream from the first stage.
12. The system according to claim 11, further comprising removing a majority of aerosol
droplets having diameters greater than 20 microns from the airflow upstream from the
anti-icing system.
13. The system according to any one of claims 9 to 12, further comprising removing aerosol
droplets having diameters greater than 20 microns from the airflow downstream from
the first stage.
14. A system (10) for use with an inlet of a gas turbine through which airflow toward
the gas turbine proceeds, the system comprising:
a first stage (50) to remove primary aerosol droplets from the airflow by coalescing
the primary aerosol droplets into secondary aerosol droplets, which are larger than
the primary aerosol droplets;
an intermediate stage (50) to remove solid particulates from the airflow;
a second water tight stage (60), disposed downstream from the intermediate stage (50),
to prevent the secondary aerosol droplets and aqueous solutions of deliquesced particulates,
which are not removed by the first stage (50) and which are re-released into the airflow
from the first stage (50), from proceeding along the airflow and to remove solid particulates
not removed by the first stage (50) from the airflow; and
a third water removal stage (70), disposed downstream from the second stage (60),
to remove from the airflow the remaining secondary aerosol droplets leaking from the
first stage, the intermediate stage and the second stage (50, 60).